FIG. 14 is a diagram illustrating a conventional example of a sensor device for sending and receiving ultrasonic waves. A sensor device 200 of this conventional example includes a piezoelectric sensor 210, a transmission circuit 220, and a receiving circuit 230. The receiving circuit 230 includes a differential amplifier 231, and transistors 232 and 233.
The transistors 232 and 233 work as switches for connecting/disconnecting between the piezoelectric sensor 210 and the differential amplifier 231 in accordance with a control signal SW. More specifically, the transistors 232 and 233 are turned off in transmission operation of ultrasonic waves and are turned on in reception operation of ultrasonic waves.
As an example of the conventional technique related to the above description, there is Patent Document 1.